1. Field of the Invention
The present invention relates to an audio signal amplifier circuit.
2. Description of the Related Art
Audio devices or electronic devices having an audio playback function include an audio signal amplifier circuit configured to amplify a weak electrical signal, and to output the electrical signal thus amplified to an electroacoustic transducer such as speakers, headphones, earphones, or the like (which will be collectively referred to as “speakers” hereafter).
In some cases, a coupling capacitor is arranged between the audio signal amplifier circuit and the speaker in order to prevent a DC current from flowing from the audio signal amplifier circuit to the speakers. With an arrangement which allows the user to detachably connect headphones or earphones to the device, if the user removes and inserts the headphones during audio playback, unexpected charging or discharging occurs at the coupling capacitor, and in some cases this current leads to an audible noise being output from the headphones. In order to avoid this problem, in some conventional arrangements, a discharging resistor is arranged on a path provided in parallel with the electroacoustic transducer. Such an arrangement including such a discharging resistor provides a charging/discharging path for the coupling capacitor regardless of whether the headphones are inserted or removed, thereby suppressing the occurrence of noise.